Zener diodes are two-terminal electronic devices which act as conventional diodes when forward-biased, i.e., with unidirectional conduction, but when reverse-biased above a certain threshold voltage, conduct in the reverse direction. The term “Zener diode” is traditionally applied to devices comprised of p-n junctions formed in conventional semiconductor materials, e.g., Si, which junctions undergo avalanche breakdown at reverse bias potentials above about 5 volts, and such devices may be utilized in voltage regulating and circuit protection circuitry.
A current (I) vs. voltage (V) plot of an idealized Zener diode is illustrated in FIG. 1, wherefrom it is evident that, when reverse-biased above a certain voltage, i.e., the Zener threshold voltage (Vzt), typically above about 5 V for Si-based devices, a sudden rise in the reverse current occurs. Thus, when forward-biased, a Zener diode functions as an ordinary rectifier, but, when reverse-biased, exhibits a knee, or sharp break, in its I-V plot. A characteristic of Zener avalanche or breakdown is that once conduction occurs under reverse-bias, the voltage across the device remains essentially constant upon further increase of reverse current, up to a maximum allowable dissipation rating. As a consequence of this characteristic behavior, Zener diodes find utility, inter alia, as voltage regulators, voltage references, and overvoltage protectors.
Zener diodes may also be utilized for protection of semiconductor memory devices in computer-related applications. However, the difficulty in tailoring (“tuning”) the Zener threshold voltage (Vzt) of conventional Si-based devices, for obtaining optimum protection in such applications, poses a significant problem.
Accordingly, there exists a need for improved Zener diodes and manufacturing methodology therefor, which methodology overcomes the above-described drawback and disadvantage associated with the difficulty in tailoring the Zener threshold voltage of conventional Si semiconductor-based Zener diodes, and which facilitates cost-effective manufacture of Zener diodes having precisely tailored (or “tuned”) Zener threshold voltages and other salient operating characteristics and parameters.